type 4 timing

[oprn]

Could someone please explain to me why the type 4 guys say to set maximum timing to 28* at 3500 RPM and the type 1 guys say 30* to 32* at 2800 RPM? What is different with the type 4 that it needs less timing and at a higher RPM?

Just reasoning this out in my mind in terms of flame travel would a larger bore not require more timing advance to get a more complete burn?

[Piledriver]

Different engine.

In detail, a T1 and a T4 share no parts, other than valve adjuster screws, and are only really similar in layout.
The T4 benefited from being designed in the late 60s vs the late 30s. Things were learned.

Different combustion chambers, better plug placement, better ports/manifolds & fuel distribution, usually more compression, better squish area.(stock vs. stock) T4 Crank had no bad harmonics and such.

The WBX is literally a watercooled T1... they kept the horrible through lifter bore oiling of the upper end, unlike the T4 which had a tangential oil feed across the top of the lifter bores, providing pressurized oil to all. WBX was running hydraulic lifters, as the t4 was likely designed to do, but they didn't fix that little detail despite using hydraulic lifters, would have helped refill them.
Not a lesson learned. They DID add mass to the crank main webs ridding them of the T1s harmonic crank whip of the center main at high RPM. (counterweights not needed... its a Boxer) as well as adopting the better T4 5 bolt crank<>flywheel joint and larger bearing. They actually improved the thrust setup on later WBX.

WBX also had different heads and combustion chambers and as I recall needed about the same total timing as a T4.
(same bore as a 2L T4) Lower timing requirements for a given bore and CR indicate better combustion chamber etc.
(needing less is better)

The DJ 2110cc WBX in Europe had 11:1 CR, made 112 HP, due it the better WBX Heron style chambers and watercooling, as well as decent fuel, looser emissions rules. US spec version made around 90HP, only huge difference was the pistons. (the chamber is mostly in the pistons on Heron heads) I suspect the 11:1 DJs needed less total timing than the almost identical but 9:1 compression MVs in the US.

[oprn]

Interesting about the WBX which was not part of the question but good to know anyway.

So being historically a type 1 guy I set up my type 4 with 8.4/1 CR, 12* initial and 31* total by 2800 RPM + 10* light throttle advance running on 87 octane. All seems good after 4 summers and about 20K km. It's not in a Bus so good there. If this is wrong what should I watch for?

The fuel economy has not been as good as expected in a light Buggy and I was putting it down to the large bore, poor head design and slow flame travel. My type 1s all did better in that aspect.

[Bruce.m]

Better engine design = less advance.

High compression, better swirl, more compact & evenly shaped chamber….. means the fuel/air burns faster & reaches peak chamber pressure faster.

Timing is all about hitting peak chamber pressure at a certain number of degrees after TDC, so advance is added to move the peak to the right time (position of piston / rod).

Any extra advance doesn’t increase power & increases the possibility of peak pressure happening too early. That creates extra heat as the conversion to kinetic energy is not optimal.

Ignition timing tuning uses the principle of the least amount of advance possible that still achieves the maximum torque.

[Piledriver]

Back it off to spec or even a tiny bit less... Anything "not stock" the factory numbers become only a starting place.
...too much timing it fights itself, they like more initial timing, up to 20 btdc, the factory distributors have "stops" that can be bent in to limit travel, the outer spring mounts can be stretched to slow advance. Its harder to explain than do, can be done through the little oval pop-off covers on the distributor. On E85 you can probably lock it down at 28 and just use vac advance, depending on your starter, I use a 9 tooth Mk4 TDI gear reduction starter with a little love from a rattail file, it can start a diesel at -20F.

More compression with stock cam means less total timing typically.
Big cams love more initial as they need it due to poor A/F mixture at low RPM.

Mind I have been running a Megasquirt EMS for ~15 years now, the only thing I use the distributor for is to hold the missing tooth wheel and Hall sensor. (allows full sequential fuel & spark, also use flex fuel automagical mix and timing tweaks etc)
Rustoleum spray paint cans provide a perfect snap-on distributor cap.

Plugs also matter, the triple electrode bosch or ngks literally put the spark a few mm further into the chamber and act like more timing, as the spark is also more exposed/unshrouded.

Fine example of something:
When I could get iridium Pulstar plugs I could run 22:1 AFR reliably at cruise.
Sadly they no longer make those, the non-iridium-fine wire versions show no benefit, so I am back to std iridiums stuck at ~18:1 AFR, LS truck coils.

The lean mix and very aggressive advance required to run that drop my CHT by 75F vs std advance and 13:1 , typically ~300F at 75MPH, 100+ degree OAT.
IIRC ideal PPP is ~20 ATDC, may differ for modern engines with highly offset bores.

[oprn]

Running 12* initial now which results in a 1400 - 1600 RPM idle fully warmed up and idle stop screws are backed all the way out. It's been suggested that the initial is too high and should be 7 to 8*.

[Bruce.m]

Running EFI I pull timing at idle but jump up to 15BTDC as soon as the throttle is cracked open.

It’s also possible to add air & pull fuel to reduce the torque.

At the top of the rpm range, I add a few extra degrees of timing as the VE table drops away from peak (engine is flowing less than the theoretical peak air flow, so the charge density is reducing & therefore can benefit from a little extra advance)

[oprn]

No EFI here, 40mm Webers. 12.5 AFR at idle, 15.5 to 16 AFR at light cruise, 13.2 to 13.4 pretty much everywhere at full throttle. Once warmed up no hesitation, bog or farts anywhere from idle to 5800 RPM. Pulls hard on the low end too. Just this high idle thing. 1000 RPM cold, 1500 ish hot.

Here is my latest map. I have been running this one for about 3 years.

[Piledriver]

Does that have any sort of "idle mode" triggered by throttle or a switch?
Killing the advance at idle will bring it right down.

If it has idle control via timing use that as well.

[oprn]

I am not aware of any idle control mode on the Mega jolt system. To accomplish what you are suggesting then I would need a micro switch on the carb linkage and a 0 - 5 volt signal to feed an unused input into the ECU?

Or would it be simpler to change a few bins in the high vacuum/low RPM end of the map?

[Bruce.m]

Only reason to have a rpm cell below 800 is so you can have a dip at 800 (idle) & more advance below as a form of anti stall. Even if it is only in the highest vacuum row.

You could also combine the highest MAP two rows as they match, giving you an extra row for lowest map side of the table

[oprn]

Yes I added the 600 RPM row on advise that it would be useful for cold starting and originally had 14* all the way up in that row. It turned out to be completely unnecessary as the engine never idles that slow even at -30*F. I could delete that whole column.

Same goes for adding a lower vacuum column. Maximum pressure we will ever see here at our altitude is 96 kPa and no engine has 100% volumetric efficiency. I suppose I might see a value outside of that if I travel to a place somewhere nearer the coast.

...or put a hair dryer on this engine...

[Piledriver]

The idea for an idle mode/row would be to have it drop the timing so you don't have a 1K idle.
Can you drop below 10BTDC on EDIS/MJ?
Have you fully closed the air bypass screws on the carbs??? No vacuum leaks?

Many NA engines exceed 100% VE, possibly even yours at some RPM.
Yamaha R1s can get >220HP out of 1 Liter, NA, careful design and good tune.
Honda K20s can exceed 240HP with stock cams, decent exhaust and good tune.

Of course making those (or much higher) HP#s is a lot easier with a snail, 14:1 CR and direct injection to ~preclude knock.

[oprn]

No this engine is not sophisticated enough to get anywhere near that kind of volumetric efficiency. It's a stocker plus.

I can drop below 10* as far as I know. Haven't tried but I see no reason why not.

No vacuum leaks. No I have not played with the air bypass screws. They still have the factory settings and factory installed block off plugs. I have been reluctant to mess with that but I am about to get over my hesitation and pull those plugs to see what is behind them. That is the plugs immediately to the left and right of the idle mixture screws.

[Piledriver]

10 BTDC is EDIS base timing, unplug the EDIS connection to the ECU, that's what you get.
I looked into using EDIS years ago before I realized MS2Extra could do full sequential fuel/spark on a 4 cylinder, and even MS1Extra could do sequential COPs on a /6.....but I have slept since then

For B&G MS1 firmware early days it was the only way to go with COPs, even if they are waste spark.
Probably true in 2002.

The screws/locknuts for the bypass air are just outboard of the idle mix screws.
(had to dig out my 44IDFs)

You don't have them, so nothing to adjust.
Don't pull the caps, likely just a hole.
The earlier carbs had them, screws/locknuts quite visible.